The present invention relates to the electrical discharge machining of rotary dies or the like from workpieces which are bodies of revolution and, more particularly, to an improved means for removing from the EDM machining zone the waste particles of metal eroded from the workpiece.
As is disclosed in my U.S. Pat. No. 3,542,993, a rotary die may be electro-erosively machined from a plain cylindrical workpiece by forming a flat electrode with a negative impression of the surface pattern desired to be imparted to the die. The workpiece and matrix electrode are then moved relative to one another in order to sequentially bring longitudinal traces of the rotating cylindrical workpiece into registration with transverse traces of the matrix surface in the proper spark gap relationship. During the machining process, the dielectric and coolant liquid is preferably continuously circulated through the tank in which the machining takes place.
This process may be performed on a wide variety of EDM machines in which the matrix electrode is preferably held horizontally, as on a vacuum table, for traversing movement past a workpiece that rotates thereover. A graphite electrode is preferred since it can be readily machined into a pattern of grooves or the like to define a flat development of a negative impression of the die pattern desired to be machined into the smooth cylindrical surface of the workpiece. However, despite the continuous recirculation of the machining fluid, some of the particles of metal electro-erosively removed from the workpiece settle within the depressions of the matrix, as well as being dispersed in the tank. As a result, the matrix pattern is gradually deformed and successive workpieces are correspondingly defectively machined.